Isomers

There are numerous examples of structural isomers in chemistry and isomers of a certain compound have different physical and chemical as well as physiological properties. Thus, for example in the field of toxicology, some isomers possess toxicity which differ by several orders of magnitude.

Ninety-five groups of various isomeric compounds have been investigated and in all cases the GC-UV method was able to distinguish clearly between structural isomers. However, when the analysis involves various straight or branched alkyl chains the identification is complicated. For difficult identifications like these derivative functions can be applied in order to enhance differences in spectral details and thus distinguish between isomers not resolved by comparing the absorbance spectra alone. Some groups, like nonaromatic halogenated hydrocarbons and nonaro-matic alcohols, show minimal differences. Nevertheless, they are still distinguishable and the first derivatives of their spectral curves give clear shifts of & 2-3 nm in the absorption maxima and minima.

Figure 7 Four chromatograms after the analysis of a dust sample. (A) The upper trace shows the total ion current (TIC) obtained from the analysis of 10 mg dust by means of GC-MS linked to the thermal desorption unit. The next three traces show the chromatograms based on first derivatives for (B) 187-190 nm, (C) 187-220 nm and (D) 238-244 nm wavelength ranges from the analysis of 6 mg dust by means of GC-UV. The peaks indicated 1-5 were identified using GC-MS and the peaks indicated by 6-8 by GC-UV. The identification results are given in the text.

Figure 7 Four chromatograms after the analysis of a dust sample. (A) The upper trace shows the total ion current (TIC) obtained from the analysis of 10 mg dust by means of GC-MS linked to the thermal desorption unit. The next three traces show the chromatograms based on first derivatives for (B) 187-190 nm, (C) 187-220 nm and (D) 238-244 nm wavelength ranges from the analysis of 6 mg dust by means of GC-UV. The peaks indicated 1-5 were identified using GC-MS and the peaks indicated by 6-8 by GC-UV. The identification results are given in the text.

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